We propose to isolate and characterize immune complexes that occur in the serum of women with breast cancer. We will use a newly developed multiple assay methodology which isolates individual immune complex species, and provides a method for dissociation and characterization of individual components of the isolated immune complex. Characterization studies will include: (1) Size of isolated complex (2) Immunoglobulin type (3) Antigen type (4) Antigen specificity (5) Antibody specificity (6) Complement binding status. We have available to us three purified antigens believed to be associated with the development of human breast cancer. These three antigens are: (1) mouse mammary tumor virus glycoprotein 52 (2) human breast reverse transcriptase (3) B2-microglobulin associated breast tumor antigen. In all cases specific antibodies to these antigens have been identified in the sera of breast cancer patients. In two case (gp52 and B2 associated) a specific cell mediated immune response has been detected using leucocytes of breast cancer patients. We will analyze isolated antigens and antibody components of breast cancer immune complexes for immune identify or relatedness to these three breast cancer antigens and/or their specific antibodies. In addition to the purified breast antigens, we will utilize for antigen specifity studies partially purified preparations obtained from: (1) disrupted mouse mammary tumor virus (2) solubilized membrane fractions of human breast cancer (3) disrupted high density ( 1.20) particles from human milk (4) fractions of ammonium sulfate precipitates obtained from urine of metastatic breast cancer patients and (5) partially purified fractions of breast cycst fluid. If immune reactivity is detected with crude mixtures to isolated and dissociated antibody components of breast cancer complexes, further purifying studies will be undertaken in an attempt to identify the immune reactive molecule in the mixture. These studies could identify an antigen/antibody system that may be clinically useful as an early immunodiagnostic reagent.